Pulse-to-revolution converter for converting a variable pulse frequency into a proportional rotation speed of a shaft

ABSTRACT

By providing a conventional pulse-to-revolution converter comprising a motor control circuit and a tacho signal negativefeedback loop with an additional negative-feedback loop an exact ratio is obtainable between the variable pulse repetition frequency of a pulse train and the rotation speed of a rotating shaft coupled to the motor. The shaft carries a shaft position pick-up which via a switching device operates a correction signal source.

United States Patent 1191 1111 3,778,693 Korteling Dec. 11, 1973 [5PULSE-TO-REVOLUTION CONVERTER 3,500,160 3 1970 Sommer 318/318 x FORCONVERTING A VARIABLE PULSE 33 FREQUENCY A PROPORTIQNAL 3:331:0O6 7/1967SAZAAQIQL'IIIII 318/314 ROTATION SPEED OF A SHAFT 3,424,966 1/1969Webb 1. 318/314 75 Inventor; Aar-t i Korteling Emmasingel, 3,522,5038/1970 Feulner 318/314 Eindhoven Netherlands 3,577,056 5/1971 Tsu ikawa318/314 [73] Assignee: U.S. Philips Corporation, New

York Primary Examiner-A. D. Pellinen Attorney-Frank R. Trifari [22]Flledz Aug. 30, 1972 [21] Appl. No.: 285,024

[57] ABSTRACT [30] Forelgn Apphcauon Pmmty Data By providing aconventional pulse-to-revolution con- Sept. 6, 1971 Netherlands 7112272verter comprising a motor control circuit and a tacho signalnegative-feedback loop with an additional nega- [52] US. Cl. 318/314,318/326 tive feedback loop an exact ratio is obtainable [51] 1118. C1."02p 5/16 tween the variable pulse repetition frequency of a [58] Fleld01 Search 318,314, 318, 326, pulse train and the rotation speed of arotating Shaft 318/327 345 coupled to the motor. The shaft carries ashaft position pick-up which via a switching device operates a [56]References Cted correction signal source.

UNITED STATES PATENTS 3,008,075 11/1961 Scott 318/314 5 Claims, 2Drawing Figures FREQUENCY T0 DEVICE VOLTASRQONVERTER COMPARATORAMPLIFIER? 81101011 10 3 6 A ,1 1 D V SHAFT CORRECHON SIGNAL GENERATORENERATOR SWITCHING mm 1 1 I913 FREQUENCY T0 VOLTAGE CONVERTER J'LItAMPLIFIER ATOR COMPARATOR A CORRECTION SIGNAL GENER -16 Fig.1

SWITCHING DEVICE PULSE-TO-REVOLUTKON CONVERTER FOR CONVERTING A VARIABLEPULSE FREQUENCY INTO A PROPORTIONAL ROTATION SPEED OF A SHAFT Theinvention relates to a pulse-to-revolution converter for converting avariable pulse frequency into a proportional speed of rotation of anoutput shaft, which converter comprises a pulse frequency-to-voltageconverter which feeds a supply circuit for a motor which is providedwith tacho-signal negative feedback and the rotor of which is coupled tothe output shaft.

In control technology it is known to feed a motor via an amplifier andto derive from the motor a tachosignal which is a measure of the speedof the motor and to return this signal as a negative-feedback signal tothe amplifier, resulting in a motor speed which is substantiallyproportional to the input voltage for the amplifier. This principle isused in some record players.

If the quantity to be converted is not the amplitude of an input voltagebut the frequency of an alternating voltage or a pulse train, in somecases synchronous motors or stepping motors may be used. However, whenthe frequency range is too large or the frequencies are too high, thesemotors either cannot be used or can only be used in conjunction withcomplicated circuits, such as frequency converters.

An obvious solution of this problem is to convert the frequency to avoltage which is supplied to a motor control amplifier of theaforementioned type which is provided with tacho negative feedback.However, the accuracy of such a system is poor. Furthermore, in someuses the temperature may have an excessive influence, and tolerances ofcomponent parts play important roles in the process of exact conversionof frequency to revolutions.

It is an object of the present invention to avoid the said disadvantagesand to provide a pulse-to-revolution converter of the type described atthe beginning of this specification which is characterized in that anegativefeedback loop is provided from a signal generator which is acoupled to the output shaft and supplies a shaft position signal to aswitching device which is connected to the input of the converter andthe output of which switches a correction signal source which supplies acorrection signal to the pulse-frequency converter, thenegative-feedback control being such that the instant at which a shaftposition signal occurs lies within a repetition period of the inputpulses.

The advantage of a pulse-to-revolution converter according to theinvention is that from the output shaft a quantity is derived whichexactly depicts the shaft position and compares it with the input pulsefrequency, compelling the control circuit to adjust itself. Thecorrection signal will be adjusted so that variations in the motor load,drift of values of the component parts of the frequency-to-voltageconverter, of the correction signal generator, of the amplifier circuit,in the tacho signal generator and in the motor due to ageing ortemperature variations are compensated for.

The invention is based on the recognition that, with properproportioning, in a desired speed or frequency range the phasedifference between the input frequency and the frequency of the shaftposition signal per cycle may be utilized to control a correctioncontrol circuit capable of compensating for the aforementionedvariations.

A preferred embodiment starts from a fixed correction quantity which ineach cycle is supplied in the control circuit and providessynchronization by the duration of the time during which it isoperative. For this purpose a pulse-to-revolution converter according tothe invention is characterized in that the switching device is aflip-flop which is set to one state by the shaft position signal and tothe other state by an input pulse, and in that the correction signalsource includes a semiconductor switch which is controlled by theflip-flop and which switches a correction quantity into circuit and outof circuit, this correction quantity influencing the pulse-frequencyconverter.

The correction quantity may, for example, influence the timing circuitof the monostable multivibrator which is included in many knownconverters for converting a pulse frequency into a direct voltage ordirect current. For example, a resistor may be connected in series or inparallel with the discharge resistor of a RC- combination in the timingcircuit, or a discharge current source may have its value changed.

Alternatively, the circuit which has an integrating function forsupplying the output direct voltage or direct current may be influencedby changing its charge circuit or discharge circuit.

It should be noted that the tacho-signal may be obtained in many knownmanners, for example by means of a tachogenerator coupled to the motoror to the output shaft, via an electronic subtraction circuit, as willbe described hereinafter, by the use of a direct-current motor providedwith permanent magnet energization which is connected as a generator fora short period, the voltage generated being stored, or by using theshaft position signal in conjunction with a frequencyto-voltageconverter. The signal generator which determines the shaft position mayalso be of a known type: an apertured disk in conjunction with a lampand a photocell, a ring of teeth in conjunction with an inductivepick-up, a magnet on the shaft in conjunction with a reed contact or aresistor sensitive to a magnetic field, while use may also be made ofthe commutation signal which can be derived from direct-current motorsby means of brushes or Hall plates.

An embodiment of the invention will now be described, by way of example,with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 is a block diagram of a pulse-to-revolution converter accordingto the invention, and

FIG. 2 is a detailed circuit diagram of an electric shaft in which apulse-to-revolution converter according to the invention is used.

Referring now to FIG. 1, a pulse train 18 is applied to an inputterminal 1 of the pulse-to-revolution converter. This signal is fed to aconverter 2 for converting a pulse frequency into a direct voltage andalso to a switching device 13. The converter 2 delivers a directvoltagesignal the mean value of which is related to the repetition frequency ofthe pulse train 18. This directvoltage signal is applied to a firstinput 4 of a comparator 3. To a second input 5 of this comparator thereis applied through a lead 19 connected to a motor 9 a direct-voltagesignal which is derived from the motor and the amplitude of which isproprtional to a number of revolutions, i.e. the speed of rotation, of ashaft 10 coupled to the rotor of the motor 9. The difference between thetwo signals at the inputs 4 and 5 produces a control signal at theoutput 6 of the comparator 3,

which signal is applied to an amplifier supply circuit 7 which feeds themotor via an input 8, causing the motor to assume a given speed. In someuses a very compact unit is obtainable by using a direct voltage and adirectcurrent motor. The motor control, which comprises the comparator3, the amplifier 7, the motor 9 and the tacho negative feedback loop 19,may also be suitable for an alternating voltage, in which case thecontrol signal applied to the input 4 must have a suitable value andform.

A signal generator 11 provides a shaft position signal, i.e. a signalwhich is related to the rotation of the shaft through a predeterminednumber of degrees. This signal is applied through a lead 20 to an input12 of the switching device 13. The difference in frequency between thepulse train 18 applied to an input 14 and the shaft position signalapplied to the input 12 provides a control signal which via a lead 15 isapplied to a correction signal generator 16 which provides a correctionsignal to a control input 17 of the converter 2.

In a suitable embodiment the amplifier control circuit 3-7-9-19 may beadjusted so that, with the input 17 of the converter 2 beingopen-circuited, the motor 9 will run at too high a speed or at too low aspeed. Hence, a correction signal must be applied to the input 17 whichreduces or increases respectively the value of the control voltage to beapplied to the input 4 of the comparator 3. This correction signal mayhave a constant value and a variable duration. The variable duration isobtainable by switching the correction signal by means of a switch whichis operated by a bistable switching device 13 which changes state eachtime a pulse is applied to its input 14 and is reset each time a shaftposition signal is applied to the input 12. Thus control is effected byphase shifting of the two signals at the inputs l2 and 14.

FIG. 2 shows a practical embodiment in which a shaft S is required torun in synchronism with a shaft 8,. The shaft 8, may be the propellershaft of a motor car and the shaft S, may be coupled to a conventionalspeedometer-odometer commonly used in automobiles. lnstead of themechanical flexible cable an electric shaft coupling is obtained whichhas many known advantages, such as no mechanical wear and failure andfreedom in the disposition of the componentparts.

On the shaft 8, is mounted a magnet M,, which in a giveri, shaftposition closes a reed contact RB As a result the level at the input ofa logic circuit A which is a NAND-gate, is changed from high to low. Thegate A is connected as a buffer to avoid current transients due to thecontact R8,, and the output of A, also changes from high to low. Thisactivates a monostable circuit comprising a capacitor C a resistor R,and a transistor T which results in that the transistor T is temporarilycut off. Consequently a transistor T becomes conductive, because itsbase is enabled to draw current via the collector resistor R of thetransistor T from a stabilized supply circuit comprising a Zener diodeZ,, a series resistor R and a supply source +V,,. The temporaryconductivity of the transistor T activates the current source comprisinga Zener diode Z an emitter resistor R 9 and a transistor T, As a result,a fixed charge is supplied to a storage capacitor C, which has adischarge resistor R Thus, the operation of the arrangement consists inthat at each input pulse a fixed charge is supplied to the capacitor Cwhich can leak away through the resistor R so that at the base of atransistor T there is set up a voltage which is in a more or lessproportional ratio to the pulse frequency.

A motor M has an output shaft 8-,; to which is secured a magnet M whichin a given shaft position energizes a reed contact RE,.

A comparator comprising transistors T and T which have a common emitterresistor R compares the voltage across the capacitor C with thecollector voltage of a transistor T which voltage is to be proved to besubstantially equal to the electromotive force EMF which is produced bythe direct-current motor itself and is proportional to the speed of themotor. The difference signal controls a transistor T, which in turncontrols a power transistor T the collector circuit of which includesthe motor M and a series resistor R The voltage across the motor isdetermined by:

mntor EMF m m,

where 1,, is the motor current and R,,, is the internal resistance ofthe motor. The voltage across R is:

m l5 'm m,

where I is the collector emitter current of the transistor T and R isits emitter resistor. The collector circuit of this transistor includesa resistor R across which a voltage 1 R is set up.

The voltage between the collector of T and earth is:

This circuit comprising three resistors and one transistor provides thetacho-signal required in this pulse-torevolution converter with asufficient degree of accuracy.

The correction signal for exact synchronisation is supplied by anadditional leakage resistor R, which is connected in parallel with acombination R C and which is switched intocircuit and out of circuit bymeans of a transistor T The transistor T is rendered conductive bycurrent supplied via a resistor R and a diode D when the diode D iscutoff owing to the output of a NAND gate A, being high. The latter isthe case when the reed contact RE is closed and, via a buffer A and adifferentiating circuit R C applies a trigger pulse to the gate A NANDgates A and A, form a flip-flop. When the next trigger pulse which isproduced by a differentiating circuit R C and by the drop of thepotential level at the output of the gate A, from high to low owing tothe closure of the reed contact RE,, is applied to the input of the gateA the flip-flop A A changes state, the output of A, falls from a highlevel to a low level, the transistor T is cut off and the leakageresistor R is switched out of circuit.

In a practical embodiment control is effected in a pulse repetitionfrequency range between a few Hz and 60 Hz, and in each cycle theleakage resistor R may provide a slope correction for the RC combinationR C of between 5 percent and 15 percent, depending upon the motor andthe motor load. In the said frequency range exact synchronization iseffected not only when the frequency changes upwards or downwards,

but also when the converter is suddenly switched to a given pulsefrequency.

I claim:

1. A pulse frequency-to-revolution converter, comprising a motor havinga rotational speed responsive to variations in input voltage and havingan output shaft, an input pulse frequency-to-voltage converter forconverting input pulses to voltage levels, a voltage supply circuitconnecting the pulse frequency to voltage converter to the motorproviding the motor with a voltage corresponding to the output of thepulse frequency-tovoltage converter, a tacho-signal negative feedbackmeans connected between the motor and the supply circuit, a shaftposition negative feedback loop connected to the motor shaft forproviding pulses corresponding to the motor shaft position, a switchingdevice connected to the shaft position negative feedback loop forproviding shaft position switching signals, and a correction signalsource connecting the switching device to the pulse frequency-to-voltageconverter for providing correction signals to the pulsefrequency-to-voltage converter in order to maintain the instant at whicha shaft position signal occurs within a repetition period of the inputpulses.

2. Pulse-to-revolution converter as claimed in claim 1, wherein theswitching device is a flip-flop which is set to one state by the shaftposition signal and to the other state by an input pulse, and in thatthe correction signal source includes a semiconductor switch which iscontrolled by the flip-flop and switches a correction means into and outof circuit, this correction means influencing the pulse frequencyconverter.

3. Pulse-to-revolution converter as claimed in claim 2, whereby thepulse frequency-to-voltage converter converts the pulse frequency into adirect voltage and includes a monostable multivibrator, characterized inthat the correction means is connected to the timing circuit of themonostable multivibrator.

4. Pulse-to-revolution converter as claimed in claim 2, wherein thepulse frequency-to-voltage converter is a pulse frequency-to-directvoltage converter comprising a current source which is controlled ateach input pulse for a fixed period of time, a parallel combination of astorage capacitor and a resistor connected to the current source, thecorrection means influencing the amplitude of the current from thecurrent source.

5. Pulse-to-revolution converter as claimed in claim 2, wherein thepulse frequency-to-voltage converter comprises a pulsefrequency-to-direct voltage converter, comprising a parallel combinationof a storage capacitor and a discharge circuit across which the outputdirect voltage may be taken, the correction means comprising a resistorwhich influences the charge of the storage capacitor,

5333" UNITED STATES PATENT omen CERTIFICATE OF CORRECTION Patent,778,693 Dated December 11, 1973 It is certified that error appears inthe above-identified patent and that said Letters Patent are herebycorrected as shown below:

Col. 1, line 42, after "is" cancel "a":

C01. 4, linev 28, cancel the minus signs in the equation;

line 36, I R R R 3 R /R should read Signed and sealed this 16th day ofApril 197M.

( EAL) Attest:

EDWARD I-'I.FLETC ER,JR. C. MARSHALL DANN Atte sting OfficerCommissioner of Patents 51 513 UNITED STATES PATENT OFFICE CERTIFICATEOF CORRECTION Patent No, ,778,69 Dat d December 1]., 1973 Inventor) AARTGERRIT KORTELING It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Col. 1, line 42, after "is" cancel "a":

C01. 4, line 28, cancel the minus signs in the equation;

line 36, "R R R R /R should read l3 4 Rm 15 Signed and sealed this 16thday of April 1971+.

m Attest:

EDWARD I LFLETCERJR. C. MARSHALL DANN Attesting Officer Commissioner ofPatents

1. A pulse frequency-to-revolution converter, comprising a motor havinga rotational speed responsive to variations in input voltage and havingan output shaft, an input pulse frequency-tovoltage converter forconverting input pulses to voltage levels, a voltage supply circuitconnecting the pulse frequency to voltage converter to the motorproviding the Motor with a voltage corresponding to the output of thepulse frequency-to-voltage converter, a tacho-signal negative feedbackmeans connected between the motor and the supply circuit, a shaftposition negative feedback loop connected to the motor shaft forproviding pulses corresponding to the motor shaft position, a switchingdevice connected to the shaft position negative feedback loop forproviding shaft position switching signals, and a correction signalsource connecting the switching device to the pulse frequency-to-voltageconverter for providing correction signals to the pulsefrequency-to-voltage converter in order to maintain the instant at whicha shaft position signal occurs within a repetition period of the inputpulses.
 2. Pulse-to-revolution converter as claimed in claim 1, whereinthe switching device is a flip-flop which is set to one state by theshaft position signal and to the other state by an input pulse, and inthat the correction signal source includes a semiconductor switch whichis controlled by the flip-flop and switches a correction means into andout of circuit, this correction means influencing the pulse frequencyconverter.
 3. Pulse-to-revolution converter as claimed in claim 2,whereby the pulse frequency-to-voltage converter converts the pulsefrequency into a direct voltage and includes a monostable multivibrator,characterized in that the correction means is connected to the timingcircuit of the monostable multivibrator.
 4. Pulse-to-revolutionconverter as claimed in claim 2, wherein the pulse frequency-to-voltageconverter is a pulse frequency-to-direct voltage converter comprising acurrent source which is controlled at each input pulse for a fixedperiod of time, a parallel combination of a storage capacitor and aresistor connected to the current source, the correction meansinfluencing the amplitude of the current from the current source. 5.Pulse-to-revolution converter as claimed in claim 2, wherein the pulsefrequency-to-voltage converter comprises a pulse frequency-to-directvoltage converter, comprising a parallel combination of a storagecapacitor and a discharge circuit across which the output direct voltagemay be taken, the correction means comprising a resistor whichinfluences the charge of the storage capacitor.